The present invention relates to a tissue oxygen measuring system, and more particularly to such a system for automatically measuring at least one of cerebral blood flow, cerebral blood volume, and a response of cerebral blood volume to change in arterial carbon dioxide tension.
In general, in diagnosing the function of a body organ, such as the cerebral tissues, the fundamental and important parameters to measure are the oxygen quantity in the body organ and the organ's utilization of oxygen. Supplying body organs with a sufficient quantity of oxygen is indispensable for the growth ability of fetuses and new-born infants. If the supply of oxygen to a fetus is insufficient, the probability that the fetus will not survive or that the new-born infant will die is high. Even if the newborn infant lives, the serious problems may remain as a result of lack of a sufficient amount of oxygen. The insufficiency of oxygen affects every body organ, but especially causes serious damage in the cerebral tissues.
An oxygen quantity measuring system by near infrared ray (hereinafter referred to as "NIR oxygen measuring system") has been proposed in the art as disclosed, for example, in Japanese Laid-Open Patent Publication No. 63-275324. Briefly, in the NIR oxygen measuring system, near infrared rays (NIR) of selected wavelengths are directed through a flexible fiber optic bundle into one side of the head. Light emerging from the opposite side of the head is conveyed by an identical bundle to a photomultiplier tube operating in photon-counting mode. A computer calculates the changes in optical absorption at each wavelength and converts these into changes in oxy- and deoxyhemoglobin concentration (.DELTA.[HbO.sub.2 ] and .DELTA.[Hb]). Near infrared spectroscopy enables transillumination of the intact head and offers non-invasive quantization of cerebral blood volume.
It has also been proposed to quantify clinically important parameters by means of the NIR spectroscopy, which parameters including cerebral blood flow (CBF), cerebral blood volume (CBV), and a response of cerebral blood volume to change in arterial carbon dioxide tension (hereinafter referred to as "CO.sub.2 response"). These parameters are clinically important for undergoing therapy for particularly newborn infants who have various cerebral lesions. Actual measurements of CBF, CBV and CO.sub.2 response have proven the clinical importance of these parameters. The ranges of measured values in each parameter are notably different between newborn infants with normal brains and infants with brain injury born, as reported in the publications cited below.
Measurements of CBF, CBV, and CO.sub.2 response will be described.